Effects of laminin-treated membrane culture inserts on the growth of bovine oocyte-granulosa cell complexes collected from early antral follicles.

Growing bovine oocytes represent a potential source of embryos, but this has not been adopted in practice. Although several offspring were produced following a two-week culture period, further optimization of the culture system is required. In vivo, the outermost granulosa cell layer is in direct contact with the basement membrane (BM); however, this interaction is absent in cultured oocyte-granulosa cell complexes (OGCs). Since the BM is known to have regulatory roles, this study examined the effects of BM components on oocyte growth by treating membrane inserts with laminin, a major BM constituent, or with the laminin-containing protein mixture Matrigel®. OGCs containing growing oocytes (90-106 μm in diameter) were cultured from Day 0 to Day 14 on plain membranes or on membranes with spots of Matrigel or laminin. A modified minimum essential medium α supplemented with 5% fetal bovine serum, 4% polyvinylpyrrolidone (average molecular weight, 360,000), steroid hormones, and 3 mM hypoxanthine was used. Granulosa cell migration was more pronounced in the treated spots, particularly in the Matrigel-treated group where migration extended across the entire treated area. Oocyte volume increased to 147% in the control group, 158% in the Matrigel group, and 160% in the laminin group, with Day 1 values normalized to 100%. Oocytes cultured on laminin-treated membranes were significantly larger than those in the control group (P < 0.05). Following in vitro fertilization, approximately 5% of the oocytes in each group developed to the blastocyst stage. Overall, the interaction between granulosa cells and laminin-treated membranes positively influenced the growth of bovine oocytes in vitro.